It is well recognized that short term and long term exposures to gaseous pollutants including ozone can alter the structure and function of the airways. However, the exact mechanisms by which airway injury leads to abnormal function remains to be clarified. We have previously shown (years 04 and 05) that inhaled ozone impairs airway mucus clearance, that this impairment is primarily due to a defect in epithelial secretion, that it is temporarily related to airway inflammation and that it can be mimicked by selected inflammatory mediators. We now propose to test the central hypothesis that all three manifestations of ozone-induced airway injury, i.e. airway smooth muscle hyperresponsiveness, mucosal dysfunction, and microvascular hyperemia and leakage are causally related to airway inflammation. With a set of in vivo and in vitro studies involving sheep exposed to intermediate levels of ozone on a short-term basis (1 ppm for 2 hrs), we will 1) determine if markers of inflammation (leukocyte, chemical mediators) associated with airway hyperresponsiveness in vivo can produce airway smooth muscle hyperesponsiveness in vitro and this can be modified by anti-inflammatory agents, 2) identify the component of mucociliary interaction which is most severely impaired and determine which imflammatory mediators play a putative role, 3) demonstrate the possibility of sequential activation of inflammatory products mediating airway epithelial cell dysfunction, and 4) characterize the role of inflammatory mediators in the microvascular responses of the airway mucosa. Long term exposure to ozone (0.5 ppm, 4 hrs/day, 5 days/week, 6 weeks) will be employed to test the secondary hypothesis that disruption of the airway epithelium causes airway smooth muscle hyperresponsiveness because of a decreased production of epithelium derived relaxant factors. By interrelating the cytologic and biochemical indices of airway inflammation with the various physiologic endpoints and by the use of appropriate antagonists, we expect to obtain interpretable data with which to test the basic premise underlying this proposal. We believe that the results of this investigation will provide useful information on the pathogenesis of ozone-induced airway injury, and that some of this information can be extrapolated to airway disease in general and form the basis for pharmacologic intervention.